The cytoplasm comprises cytosol – the gel-like substance enclosed within the cell membrane
– and the organelles – the cell's internal sub-structures. All of the contents of the
cells of prokaryote organisms are contained within the cytoplasm. Within the cells of
eukaryote organisms the contents of the cell nucleus are separated from the cytoplasm,
and are then called the nucleoplasm. The cytoplasm is about 80% water and usually colorless.
It is within the cytoplasm that most cellular activities occur, such as many metabolic pathways
including glycolysis, and processes such as cell division. The inner, granular mass is
called the endoplasm and the outer, clear and glassy layer is called the cell cortex
or the ectoplasm. Movement of calcium ions in and out of the
cytoplasm is thought to be a signaling activity for metabolic processes.
In plants, movements of the cytoplasm around vacuoles are known as cytoplasmic streaming.
Constituents The cytoplasm has three major elements; the
cytosol, organelles and inclusions. Cytosol
The cytosol is the portion of the cytoplasm not contained within membrane-bound organelles.
Cytosol makes up about 70% of the cell volume and is composed of water, salts and organic
molecules. The cytosol is a complex mixture of cytoskeleton
filaments, dissolved molecules, and water that fills much of the volume of a cell. The
cytosol also contains the protein filaments that make up the cytoskeleton, as well as
soluble proteins and small structures such as ribosomes, proteasomes, and the mysterious
vault complexes. The inner, granular and more fluid portion of the cytoplasm is referred
to as endoplasm.
Due to this network of fibres and high concentrations of dissolved macromolecules, such as proteins,
an effect called macromolecular crowding occurs and the cytosol does not act as an ideal solution.
This crowding effect alters how the components of the cytosol interact with each other.
Organelles
Organelles, are usually membrane-bound, and are structures inside the cell that have specific
functions. Some major organelles that are suspended in the cytosol are the mitochondria,
the endoplasmic reticulum, the Golgi apparatus, vacuoles, lysosomes, and in plant cells chloroplasts.
Cytoplasmic inclusions
The inclusions are small particles of insoluble substances suspended in the cytosol. A huge
range of inclusions exist in different cell types, and range from crystals of calcium
oxalate or silicon dioxide in plants, to granules of energy-storage materials such as starch,
glycogen, or polyhydroxybutyrate. A particularly widespread example are lipid droplets, which
are spherical droplets composed of lipids and proteins that are used in both prokaryotes
and eukaryotes as a way of storing lipids such as fatty acids and sterols. Lipid droplets
make up much of the volume of adipocytes, which are specialized lipid-storage cells,
but they are also found in a range of other cell types.
Controversy and research The cytoplasm, mitochondria and most organelles
are contributions to the cell from the maternal gamete. There is considerably less research
and understanding on cytoplasmic inheritance/maternal inheritance and mitochondrial DNA compared
to the cell nucleus and genomic DNA. Historically, there has been neglect of researching whatever
has been labeled female. The cytoplasm is one organelle that has been labeled feminine.
The cytoplasm/nucleus being labeled as feminine/masculine follows the example of egg/sperm being gendered;
both cytoplasm and egg are considered nonresistant to the efforts and pursuits of the active
nucleus and sperm. The "passivity of the egg becomes the passivity of the cytoplasm." Contrary
to the older information that disregards any notion of the cytoplasm being active, new
research has shown it to be in control of movement and flow of nutrients in and out
of the cell by "viscoplastic behavior and... a measure of the reciprocal rate of bond breakage
within the cytoplasmic network." See also
Protoplasm, a general term for cytoplasm Syntitium, a cytoplasmic region
References
External links Luby-Phelps K. "Cytoarchitecture and physical
properties of cytoplasm: volume, viscosity, diffusion, intracellular surface area". Int
Rev Cytol. International Review of Cytology 192: 189–221. doi:10.1016/S0074-7696(08)60527-6.
ISBN 9780123645968. PMID 10553280.